1. Field of the Invention
The present invention pertains to a tower or so-called jacket structure and a method of installation for supporting offshore oil and gas operations platforms.
2. Background
A wide variety of offshore support structures have been developed for use in conjunction with the development and production of oil and gas from offshore wells. In water depths up to several hundred feet fixed support structures known as "jackets" have been constructed in the form of self-supporting, skeletal towers, basically comprising three or more vertical column or leg members which are interconnected by suitable bracing. Such towers are typically secured to the sea floor by piling which is driven through the hollow leg members and secured to the leg members before installation of a deck or other structure to be supported by the jacket.
The structural requirements of prior art jackets has been such that in order for the jackets to be self supporting prior to and after installation, that the plural leg members are all made up of relatively large diameter metal pipe, thereby adding to the weight and cost of the jacket structure. The bracing required to support the pipe type leg members is also required to be relatively complex and the overall structure thereby is subject to greater wave loading when installed in the sea. In essence, the construction of prior art jackets is such that the leg members are not efficiently utilized. The jacket structure itself serves primarily as a guide and lateral support for piling which bears the actual vertical load of the deck or other structure to be supported above the surface of the sea.